Some of the more popular tennis racquet frames available today are made of fiber-impregnated resins, e.g. graphite, which are formed as tubular stock and shaped and cured in a heated mold. The tubular member is bent in the mold to define an elliptical head portion, and the opposite free ends of the tubular member then converge to form a throat area and a shaft portion that supports a handle. A bridge extends between the tubular sides in the throat area, to enclose the head portion and form an area which supports strings.
The impact of the ball upon the racket strings causes the strings and frame to deflect, thereby imparting vibration to the frame. Vibration in the racquet is undesirable and, as a result, there have been many proposals to modify the basic tennis racquet frame to attempt to reduce or more quickly dampen vibration.
One approach to this problem has been to fill the core of the racquet frame with a vibration dampening material. An example is disclosed in Fernandez et al. U.S. Pat. No. 4,413,822, in which the core or a tubular racquet frame is filled with an elastic polymer. In reality, foam cores often produce little in the way of vibration dampening. Moreover, if higher densities are used, such as needed in Fernandez, the core adds significantly to the weight of the racket.
Yuhas et al. U.S. Pat. No. 4,634,124 discloses a sports racquet in which an elastomeric dampening material is interposed between the throat piece and the adjoining legs of the frame. The dampening pieces are relatively thin and also are fastened to the frame, and thus it appears that the vibration dampening capability is limited. Yuhas also proposes, in an alternative embodiment, to reduce the vibration of the strings. In this embodiment, the strings bear against nubs of elastomeric dampening material. However, the nubs are at the support point for the strings, and thus the degree to which they can reduce string vibration is limited.
An effective vibration dampening structure for graphite and similar tubular racquet frames is disclosed in commonly owned U.S. patent application Ser. No. 049,775, filed May 12, 1987, and since abandoned. The tennis racket frame is a tubular sandwich construction in which a visco-elastic dampening sleeve is disposed between inner and outer tubular frame members of fiber-impregnated resins. With vibrating movements, opposed surfaces of the inner and outer tubular members deflect by different amounts, which is taken up in the sleeve to quickly dissipate vibration energy.
While some of the known measures do reduce racquet vibration, it would be desirable to utilize other structural features that will reduce frame vibrations further. Also, it would be desirable to provide structure that will effectively reduce vibration in the strings.